Authorities and witnesses say the attackers were among about 1,000 people, mostly men, who congregated at Cologne's central train station before breaking off into small groups that molested and robbed women.

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Ms Merkel's "open door" policy had already attracted criticism from within her party before the Cologne attacks

Victims described chaos as dozens of sexual assaults and robberies were carried out with little apparent response from the authorities around Cologne station.

Similar attacks to those seen in Cologne were also reported in Hamburg and in Stuttgart on New Year's Eve. In Bielefeld, hundreds of men tried to force their way into nightclubs, Die Welt reported (in German).

Police said several women had alleged sexual assault.

On Friday, the chief of police for Cologne was suspended. Wolfgang Albers had been accused of holding back information about the attacks, in particular about the origin of the suspects.